The invention is based on an electromagnetically actuated valve according to the general class in claim 1.
A valve is already known (DE 41 34 490 A1) that is designed as a proportioning pressure-control valve. To obtain good control behavior, the known pressure-control valve equipped with a seat valve closed without current is designed according to the solenoid plunger principle, that is, the pole body has a recess on the front side into which the basically cylindrical solenoid armature plunges more or less deeply as a function of an electric current supplied to an electrical winding enclosing the pole body. The magnetic force acting upon the solenoid armature is thereby supported by a hydraulic force in the sense of opening the seat valve, while the force of the return spring counteracts these forces.
The known valve has the disadvantage, however, that the solenoid plunger principle requires increased expenditures in the structural design of the pole body and solenoid armature. In particular, low radial tolerances are required between the solenoid armature and the pole body to prevent the formation of secondary air gaps. This, in turn, requires a costly guidance of the solenoid armature with low guidance play, because transversal forces on the solenoid armature can lead to functional failings. The known valve is therefore costly to manufacture.
Moreover, an electromagnetically actuated valve operating according to the flat-type armature principle is made known in DE 196 04 317 A1 that comprises a seat valve that is open in the non-energized state. Although this known valve is designed like a two-position valve (open, close valve), it can be moved into numerous random intermediate positions using short strokes like a proportioning valve by controlling the magnetic force that counteracts the force of a return spring and a hydraulic force, without having to comprise the expensive design of a proportioning valve, however. The main contributing features here are the design of the seat valve and the coordination of the magnetic force characteristic curve and return spring.
In contrast to the proportioning valve mentioned initially, the electromagnetically actuated valve according to the invention having the features in claim 1 has the advantage that it has the simple design of a two-position valve with a flat-type armature but behaves like a proportioning valve. Since, with the flat-type armature, the lines of flux of the magnetic circuit in the working air gap basically extend between the facing-each-other, flat front sides of pole body and solenoid armature, radial tolerances have little effect in this design. Moreover, the design of the seat valve and push-rod region contributes to a stable control behavior of the valve according to the invention working as pressure-control valve: the pressure prevailing on the side of the pressure-medium inlet supports the magnetic force to open the seat valve. Pressure medium emerging from the valve seat is directed without turbulence along the shutoff member and the push rod against the solenoid armature and exerts an opening effect. As the pressure differential between pressure-medium inlet and pressure-medium outlet decreases, this force effect diminishes, and the valve reaches a stable final position of the seat valve when the pressure at the outlet adjusted as a function of flow is reached. This control procedure takes place with dynamics and control quality that suffices for many applications.
An advantageous design of the valve according to the invention is described in claim 2.